FIG. 4 shows a prior art liquid phase crystal growth apparatus for hetero-epitaxial liquid phase growth. In FIG. 4, reference numeral 1 designates a melt boat and a lid 2 is provided on the melt boat 1 to enclose the boat 1. Reference numeral 3 designates a first melt of a compound semiconductor contained in the first room of the boat 1 and reference numeral 4 designates a second melt of a compound semiconductor having a composition different from the first melt 3 contained in the second room of the boat 1. Reference numeral 6 designates a mother boat and reference numeral 5 designates a substrate placed in a concave part on the surface of the mother boat 6. Reference numeral 9 designates a quartz tube and this quartz tube 9 is heated by a heater 10. Reference numerals 11a and 11b designate a moving rod for moving the mother boat 6 and the melt boat 1, respectively.
The prior art liquid phase growth process will be described.
FIGS. 5(a)-5(d) show a prior art hetero-epitaxial liquid phase growth method.
FIG. 5(a) shows a state where temperature adjustment is carried out. The first melt 3 and the second melt 4 are airtightly enclosed by the melt boat 1 and the lid 2 and they are positioned to one side of the substrate 5 which is placed on the mother boat 6 and are held in the melted state for a predetermined time.
Next, the entire boat, that is, the melt boat 1 and the mother boat 6 are cooled to lower its temperature at a predetermined speed, and when it reaches a predetermined temperature, the melt boat 1 is pushed by the moving rod 11b to a state shown in FIG. 5(b) such that the first melt 3 contacts the substrate 5. Then, a first layer epitaxial thin film is grown on the substrate 5.
Next, the melt boat 1 is pushed further by the moving rod 11b to a state shown in FIG. 5(c) such that the second melt 4 is made in contact with the substrate 5 on which the first layer epitaxial thin film has been grown. Then, a second layer epitaxial thin film is grown on the first layer epitaxial thin film.
Finally, the melt boat 1 is further slided by the moving rod 11b to a state shown in FIG. 5(d), and the substrate 5 is separated from the first and second melt 3 and 4, thereby completing the growth.
In the prior art example, the first layer thin film is epitaxially grown by using the first melt 3 and the second layer thin film is epitaxially grown by using the second melt 4.
In the prior art hetero-epitaxial liquid phase growth method, it is necessary to prepare a plurality of melts having different composition for the hetero-epitaxial growth. Therefore, the melt production requires a lot of work and the materials are expensive.